The present invention disclosed herein relates to a microphone, and more particularly, to an easily installable microphone for an implantable hearing aid.
According to statistics, there are more than seven billion people living around the globe. Among these, about 10% of persons suffer from hard of hearing. Here, a person who can be solved by conventional hearing aids is estimated to reach about 80% of persons that suffer from hard of hearing. Thus, the rest has a difficulty in compensation of hearing by using general air conduction hearing aids. This is done because, if the hearing is terribly deteriorated due to genetic problems, hearing loss by aging, and noise environments by construction or explosion in industrial settings, the persons who have difficulty in hearing does not understand sounds even though the sounds are amplified by using existing hearing aids. In two hearing aids that are used for the persons who cannot be satisfied by general hearing aids, one is a cochlear implant which converts sounds into electrical signals to stimulate acoustic nerves of a cochlea, and the other is a middle ear implant which amplify sound signal and then converts the amplified electrical signal into the mechanical vibration, thereby applying the amplified vibration to the auditory ossicles or a round window of the inner ear.
The cochlear implant that is commercialized in the current years to make up the largest market may be a semi-implantable hearing aid. Thus, a microphone, an amplifier, and a power source may require an external device that is attached or detached to the outside of a skin. One of widely known middle ear implant has been commercialized by MED-EL GmbH is currently available in the market. However, the commercialized middle ear implant is also the semi-implantable hearing aid up to now. Since all of the implantable hearing aids are the semi-implantable hearing aids and thus exposed to the outside, all and sundry may notice a person as a person who have difficulty in hearing in the state where the person wears the hearing aid. Thus, since the hearing aid is worn while one is out, and is separated when returning home, it is inconvenient to the user. As a result, the users that use the implantable hearing aid have been longing for completely implantable hearing aid instead of the semi-implantable hearing aid.
The most difficult technology in manufacturing of the completely implantable hearing aid may be an implantable microphone technology up to now. Major companies that manufacture the implantable hearing aids, such as Cochlear Co., Ltd., MED-EL GmbH, and Advanced Bionics Co., Ltd., have been constantly attempted to develop the completely implantable hearing aids for commercial scale. However, the commercialization of the completely implantable hearing aids has failed always due to deterioration in performance of the implantable microphone. Hereinafter, the typical implantable microphone and its limitations will be described.
(1) A completely middle ear implant has been developed by US Otologics Co., Ltd., are practically finished under way on a clinical demonstration. The implantable microphone that is used for this hearing aid may require an additional surgical operation due to the large size of microphone (a length of about 5 cm, a width of about 2.5 cm, and a depth of about 3 mm) for installing in addition to the implantation of a system body and vibrational transducer. If the above-described type microphone is used, following limitations may occur. When fingers, clothes, and pillow contact the surroundings of a skin that covers the microphone instated under a skin of ostemporale, or masticatory movement for eating foods is executed, noises may be directly applied to the microphone. Thus, it may be difficult to allow a user to hear speech sounds properly. Also, since the microphone is implanted under the skin, the microphone may be deteriorated in high frequency sensitivity.
(2) According to a TICA hearing aid (Germany) that is developed by Leysieffer, an implantable microphone is installed under a skin of an external auditory meatus. Thus, when sounds pass through a skin layer, attenuation may occur to reduce sensitivity. If the microphone is implanted at a shallow depth under the skin of the external auditory meatus to solve the above-described limitation, the microphone may not adhere to the tissues under the skin to protrude to the outside of the skin in long-term point of view. Thus, the TICA hearing aid does not put to practical use and thus is not studied any more.
(3) An implantable microphone that is proposed by Wen H. Ko may be classified into a MEMS microphone attached to a malleus behind a tympanum, a MEMS mass microphone, and a capacitive microphone. According to the method in which the MEMS microphone itself is attached to malleus which is behind the tympanum, sounds introduced through the external auditory meatus may be attenuated while passing through the tympanum to reduce the sensitivity. The MEMS mass microphone may respond acceleration velocity when the malleus itself is vibrated to generate electrical signals. However, this may be much deteriorated in a gain of low-frequency and high-frequency. Also, since the anchor has to be fixed to the wall of the middle ear cavity, a method for detecting capacitance's changes by the displacement of ossiculum that is vibrated according to the sounds by fixing an anchor to a wall of a middle ear cavity may have a difficulty in operation of implant.
(4) An Envoy system utilizes a tympanum as a vibrator of the microphone. According to this method, an anchor is formed on an end of a piezoelectric element to fix the anchor to a middle ear cavity wall to achieve displacement in which auditory ossicles such as a malleus or an incus are vibrated according to sounds as piezoelectric signals, thereby obtaining electrical signals. Also, it is necessary for a fixing process of the piezoelectric microphone by forming a hole in the middle ear cavity. Also, since feedback between an input and an output of the hearing aid occurs if the auditory ossicles are not removed, the auditory ossicles have to be physically separated. Thus, this method may be a very invasive method.